For various medical reasons, such as diagnostic tests or the like, it is often necessary for a physician to obtain a sample of a specific tissue from a patient Often, a biopsy (sample) is required from a rigid structure, such as a bone or bone marrow. Bone marrow biopsies are typically recovered with significant portions of their internal bony structure intact which allows the pathologist to provide interpretations regarding bone marrow cellularity or possible infiltration with abnormal cells.
A bone marrow sampling procedure usually includes both the collection of a core biopsy using a bone marrow biopsy needle and a fluid sample of bone marrow using an aspiration needle. The two specimens provide complementary information that is relevant for the evaluation of a variety of malignant and nonmalignant hematologic processes. The bone marrow aspiration provides a liquid sample of suspended hematopoietic progenitor cells, stromal cells, and trabecular bone fragments that can be processed for flow cytometric analysis of the bone marrow content, for cytogenetic studies, as well as for the preparation of smears for detailed morphologic evaluation of the progenitor cell morphology. The core biopsy provides accurate information regarding the status of the supporting bone, the cellularity of the bone marrow sample, and the identification of extrinsic cells as seen when the bone marrow is infiltrated with lymphoma or carcinoma.
The process of obtaining both the core biopsy and aspiration sample can produce significant pain for the patient. Specimen capturing needles, including those of the present applicant that are set forth in issued and pending applications, have been designed in an attempt to limit the manipulation of the bone marrow biopsy needle, to increase the recovery of more substantial specimens and to decrease patient pain. However, conventional needles have not been specifically designed to minimize the pain associated with the aspiration process.
Aspiration type needles have a relatively simple design. The needle typically has a sharp tip for puncturing the cortical bone and usually a hub and handle to facilitate the operators guiding the tip safely into the appropriate position. A stylet is left in place until the needle has penetrated the cortex, after which it is removed and an aspirating syringe is placed at the hub. The syringe plunger is rapidly withdrawn to quickly produce a negative pressure which is transmitted through the needle into the bone marrow space to dislodge the material and facilitate its collection into the syringe through the needle. The procedure of quickly pulling back on the plunger and producing a negative pressure usually produces significant pain often described as radiating down the leg. Since the advent of specimen capturing needles, the pain has been described by some patients as being worse than the pain associated with the bone marrow biopsy procedure. An aspirate needle that minimizes patient pain would make the bone marrow procedure more tolerable and acceptable. Moreover, an aspirate needle that minimizes pain would be especially advantageous when multiple aspirates are required to recover a sufficient quantity of bone marrow material for processing.
The exact mechanism that results in the pain and its radiation down into the lower extremity is unknown. It is hypothesized that the introduction of a negative pressure into the bone marrow space stimulates a variety of nerve fibers that results in the pain. Alternatively, simple disruption of the trabecular structure may be the source of the pain.